98greenmachine

I really didn't want to start a thread on this but I searched and searched and couldn't find anyone with a similar problem and eventual solution. Closest I came was the wranglerforum but the guy didn't have an SYE and a solution was never posted. Now that, that is over with here's the problem. 1998 XJ 6.5" short arm lift (RC), SYE, Adams rear driveshaft. I have 6 deg shims and my pinion angle is good. When I start driving no vibes but halfway through 1st gear through halfway through 2nd gear there is a vibration that starts slow and builds up til it sounds pretty bad but if I keep going it stops and never comes back again. It also doesn't do it all the time but I'd say about 80% of the time it does it. The vibration isn't in the steering or suspension cuz it doesn't feel like death wobble or anything and the steering wheel doesn't move. I replaced all the TRE's, all control arm and track bar bushings, and everything is greased and torqued to spec. I got an alignment and tires balanced but that didn't fix it. The alignment guy said my toe was 0.25 deg and my caster was 9 deg. I've read the caster at my height should be about 4.5 deg. Do you think this could be the cause of the vibration? Any other areas I should check/inspect/replace? If you need any more info on what is happening or my current setup just ask. Thanks in advance for any advice.

peep

Is the double cardigan joint of the front drive shaft in good shape. I developed a bad vibe last year within a short time. All else seemed tight and well. Was my double C needing a rebuild.

98greenmachine

You know I didn't really bother looking into that but it brings up a question I had. When in 2wd does the front shaft spin? I figured it won't only spin in 4HI and 4LO but if it spins when the front wheels are rolling cuz the pinion spins therefore spinning the front DS it could very well be it. I'll remove it and try driving without it and see if there is a difference.

Lead Foot

Front driveshaft always spins unless you have a disconnect Dana 30 or done a lock out hub conversion. 9 degrees castor is quite a bit. Most go 6-7. My guess is your front pinion isn't pointed up directly to the transfer case front output like it should be. Sounds like front driveline vibration. Remove the front driveline then take it for a spin. See if the vibration disapears.

PS. if you think your XJ rides nice right now with 6.5" lift and short arms, you should try a long arm conversion. It could really surprise you.

Kris Froehlich

98greenmachine

Well thanks for the insight guys. I removed the front driveshaft and no vibes at all. It felt so nice ha ha. So I'm gonna take it to a driveshaft shop and have them check it out and let me know what needs to be fixed. For the caster I'm gonna have to wait another week because I still have to trim my fenders. The guy at the shop said when the lower the caster it's going to move the wheels towards the rear of the jeep. Now this is just my thought and maybe you guys could shine some light on the subject but I thought if your caster was too high your pinion was too low and to fix this the upper control arms would need to be lengthened. If this is the case then wouldn't my wheels move slightly forward?

98greenmachine

And long arms are definitely on my list to do. I heard everyone say the ride on short arms is terrible but I don't find it unbearable. But definitely heard spectacular things about how a long arm setup rides.

peep

Good to hear you'v located the vibration.

98greenmachine

I know I posted about this a long time ago but thought I'd recap. I took the front DS out and vibes went away. So I took it to a DS shop in town and they said it looked fine I wasn't over extending it and the joints were good so they rebalanced it and I put it back in and the vibe was still there. So I finally got some time and research done and decided to fix my caster. My diff angle was 91 deg (9.5 deg caster) and from doing some research I found that 2 full turns of the UCA related to about 1 deg of caster change. For a 6.5" lift I need to be at about 4.5 deg caster or 85.5 deg at the diff. So ten turns later and a come a long strapped to a truck and I was sitting at exactly 85.5 deg at the diff. Took her for a spin and no vibes. Driving my jeep is sooo much more enjoyable now. Thanks for the help guys.

BlackneckOffroad

When you say "two full turns" or "ten full turns" you mean adjustable UCA's?

FOXxX

Thats what it sounds like to me...